Tensile performance and uniaxial tensile toughness of lightweight ultrahigh-performance concrete: Acoustic emission monitoring and meso-discrete analysis

This paper addresses the insufficient load-bearing capacity and cracking of concrete bridges caused by aging by investigating the influence of steel fibers on the tensile performance of lightweight ultrahigh-performance concrete (LUHPC). We systematically examined the influence of steel fiber volume fractions on the tensile toughness, first-cracking strength, tensile strength, and peak tensile strain of LUHPC and analyzed its failure mode evolution via uniaxial tensile tests. The results indicate that the failure mode of LUHPC becomes more pronounced with increasing steel fiber volume fraction. As the volume fraction rises from 0% to 3%, the fracture mode transitions from brittle single-crack failure to ductile multi-crack propagation, while the direct tensile toughness first increases and then decreases. The first-cracking strength increases from 2.8 MPa to 5.4 MPa, an improvement of 103.57%; the tensile strength rises from 4.6 MPa to 17.4 MPa, an increase of 278.26%; and the peak tensile strain grows from 750 × 10⁻⁶ to 6086.3 × 10⁻⁶, representing an enhancement of 711.51%. Based on fracture mechanics theory, integrated experimental data, and compiled literature datasets, predictive equations for the first-cracking strength, tensile strength, peak tensile strain, and uniaxial tensile toughening coefficient of steel-fiber-reinforced LUHPC were established. Three axial tensile constitutive models for LUHPC were established. Among them, a damage model developed based on acoustic emission, which correlates the damage factor with a Weibull distribution, effectively characterizes the evolution of the material's tensile performance. The proposed prediction equations and constitutive models can provide a theoretical basis for the design and application of LUHPC in lightweight, high-durability structures.